Pile driving

ABSTRACT

A pile driver includes a base and selectively operable means, such as an air cushion support system, for supporting the base in an elevated position above ground. Suitable cranes are provided for disposing a pile substantially vertically of the base with the lower end of the pile in engagement with ground adjacent the base. The base carries means which are operable in the elevated position of the base for transferring at least a substantial portion of the weight of the base to the pile. A suitable hammer is carried by the base for applying impact loads to the upper end of the pile. Where an air cushion support system is used, the system may be overpowered to cause the base to oscillate vertically through a range less than the stable hover height of the base, and at least some of the energy of such oscillation is applied to the pile to drive it into the ground. Also, where an air cushion support system is used, the space under the base may be partially evacuated after the weight of the base is transferred to the pile, thereby to increase the downward steadystate preload applied by the base to the pile.

United States Patent Anders 1 Sept. 3, 1974 PILE DRIVING [57] ABSTRACT[75] Inventor: Edward Anders Houston, A pile driver includes a base andselectively operable [73] Assignee: Global Marine Inc., Los Angeles,means Such as an air cushion Support System for P C lif porting the basein an elevated position above ground.

Suitable cranes are provided for disposing a pile sub- [22] Flled: 15,1973 stantially vertically of the base with the lower end of [2] 1 Appl.No.: 323,826 the pile in engagement with ground adjacent the base.

. The base carries means which are operable in the ele vated position ofthe base for transferring at least a [52] US. Cl 61/535, 61/63, 173/24,Substantial portion of the weight of the base to the 180/1 16 pile. Asuitable hammer is carried by the base for ap- [51] [lit- Cl E0211 7/00,EOZd 7/02, EOZd 7/18 plying impact roads to the upper end of the pile[58] Field of Search 6l/53.5, 46.5, 63; where an air cushion supponSystem is used the 180/1 117; 23 tem may be overpowered to cause thebase to oscillate vertically through a range less than the stable hover[56] References Clted height of the base, and at least some of theenergy of UNITED STATES PATENTS such oscillation is applied to the pileto drive it into 2,592,448 4 1952 McMenimen 61/465 th gr und- Also,where an air cushion support system 2,833,118 5/1958 Nixon 61/465 isused, the space under the base may be partially 2,976,693 3/1961Showalter 61746.5 evacuated after the weight of the base is transferredto 3,693,729 9/1972 Blurton et al 61/465 X; the pile thereby to increasethe downward steady- Primary Examiner-Jacob Shapiro Attorney, Agent, orFirmChristie, Parker & Hale state preload applied by the base to thepile.

29 Claims, 16 Drawing Figures Pmmensm m4 3.832858 SHEET SB? 6 PILEDRIVING FIELD OF THE INVENTION This invention pertains to pile driving,an more particularly to pile driving in which the pile is subjected to asteady-state or cyclic load of substantial magnitude onto whichconventional pile driving techniques may be superimposed.

BACKGROUND OF THE INVENTION REVIEW OF THE PRIOR ART Historically, pilesare driven into the ground by a hammering process in which series ofseparate impacts are applied to the upper end of the pile by a suitablehammer. As each impact is applied, the pile is driven into the ground byan amount which is determined by the impact energy, by the size and massof the pile, and by the resistance of the ground to penetration by thepile. Between impacts, no downward force is applied to the pile, and theground has an opportunity to recover and stabilize its resistance topenetration.

Those advances recently made in pile driving involve improvements in theapparatus used to apply impact loads to the pile. A notable example ofsuch an advance is the Bodine sonic hammer in which high frequencymechanical energy is applied to the pile for transmis sion along thepile into the ground where it is released to partially fluidize theground to a condition of reduced resistance to penetration.

Even in the case of the Bodine sonic hammer, the pile driving apparatusis conventional in that it is either a towable or self-propelled vehicle(for land operation) or barge (for marine operations). These types ofpile drivers are not well suited for use in arctic areas where greatneed now exists for pile-supported or pileprotected structures. Suchstructures are needed to facilitate development of or exploration forthe substantial reserves of oil or natural gas known or suspected toexist in the northern portions of Alaska and Canada, for example.Existing vehicular pile driving rigs arenot desirable in areas coveredby tundra because they are heavy and are destructive of the delicatetundrawhich is necessary to protect the underlying permafrost. Also, thetundra is dotted with lakes and muskeg bogs which make difficult themovement of vehicular rigs. Bargemounted pile driving rigs are notattractive economically because they can be used readily only in theshort periods in which arctic waters are free of ice.

A need thus exists for an easily moved pile driver which can be usedeffectively and efficiently on land or on water, as appropriate. Such apile driver is of general utility, but is of particular appeal in arcticareas. Also, a need exists for a wholly new approach to the process ofdriving piles.

SUMMARY OF THE INVENTION This invention provides a novel process forplacing piles in the ground. Basically, the weight (in toto or insubstantial part) of the entire pile driving rig is applied to the pile,either statically or dynamically, to significantly increase the rate atwhich the pile is driven into the ground. The application of the rigweight to the pile is in addition to the application of serial impactsto the pile by conventional apparatus. Further, the pile driving rigitself is mounted on a buoyant ground effect (air cushion) platform.Thus, while the weight of the overall rig may not be low, its effectivefootprint pressure on the ground, when supported on a cushion of air, issufficiently low and uniform that the rig may be moved readily, as bytowing, over tundra, including over muskeg bogs. For marine situations,the platform can be used in a floating state, or it can be used as itsown icebreaker in thin ice conditions, or it can be operated over thickice to drive piles.

All of the foregoing benefits and advantages are provided by proceduresand apparatus which are simple, efficient and economic.

In general terms, as to procedure, this invention provides a method fordriving piles which includes providing an elevatable base. A pile to bedriven is disposed substantially vertically through the base intoengagement with the ground below the base into which the pile is to bedriven. The base is then elevated from the ground along the pileindependently of the pile and any other piles previously driven. Then,at least a portion of the weight of the base, and of all other equipmentcarried by it, is applied to the pile, following which other drivingloads may be applied to the pile by conventional procedures, as desired.

As to apparatus, this invention provides a pile driver which includes abase and selectively operable means operable for supporting the base inan elevated position above ground and the like. The pile driver alsoincludes means for disposing a pile substantially vertically of the basein engagement with ground adjacent the base and into which the pile isto be driven. Means are operable in the elevated position of the basefor transferring substantially the entire weight of the base to a piledisposed vertically of the base.

The above mentioned and other features of this invention are more fullyset forth in the following detailed description of certain presentlypreferred embodiments of the invention, which description is presentedwith reference to the accompanying drawings, wherein:

FIG. 1 is a top plan view of an air cushion pile driver;

FIG. 2 is a cross-section view taken along line 22 in FIG. 1;

FIG. 3 is a cross-section view similar to that of FIG. 2 of another aircushion pile driver;

FIG. 4 is a perspective view of the valve and valve drive mechanism forthe pile driver shown in FIG. 3;

FIG. 5 is a fragmentary cross-section view of a cushion-air handlingmechanism for another pile driver;

FIG. 6 is a cross-section elevation view of still another air cushionpile driver according to this invention;

FIG. 7 is a fragmentary elevation view, partially in cross-section, of amodification of a portion of the pile driver shown in FIG. 6;

FIG. 8 is a fragmentary cross-section elevation view showing oneoperative state of an air cushion skirt structure useful with the piledriver shown in FIG. 3, for example;

FIG. 9 is a view similar to that of FIG. 8 showing the air cushion skirtin another operative state thereof;

FIG. 10 is a view similar to FIGS. 8 and 9 showing the skirt structureof FIGS. 8 and 9 in a fully expanded state for purposes of illustration;

FIG. 11 is a fragmentary cross-section elevation view of one operationalstate of another skirt structure useful with the pile driver shown inFIG. 3, for example;

FIG. 12 is a view similar to FIG. 11 showing the skirt structure of FIG.11 in another operational state;

FIG. 13 is a cross-section elevation view similar to that of FIGS. 11and 12 showing the skirt structure in still another operational statethereof;

FIG. 14 is a fragmentary elevation view of a portion of the skirtstructure shown in FIGS. 8, 9, and

FIG. 15 is an elevation view, partially in crosssection, of a towtractor equipped with a negative pressure-sealing air skirt to enhancethe drawbar pull of the tractor; and

FIG. 16 is an elevation view, partially in section, of a positioningtable utilizing a positive and negative pressure-sealing air skirt.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS Referring to FIGS. 1 and 2,an air cushion pile driver 10 has a floatable platform-like base 11which is of generally U-shaped platform configuration around a slot 12which extends from about the base center of area to an adjacent edge ofthe base, such as rear edge 13. In FIG. 1, base 11 is shown to be ofgenerally square configuration, but it is within the scope of thisinvention that the base may be a rectangular, oval, circular or anyother configuration desired. It is also possible that the opposing sidesof the slot may diverge relative to each other from the inner end of theslot to that peripheral edge of the platform to which the slot opens.

An air cushion skirt assembly 15, which preferably is of the segmentedtype, is connected to the base along its entire periphery, includingalong the extent of slot 12, for enclosing a space 16 between the bottom17 of the base and the surface of ground 18 over which the pile drivermay be disposed either in use at or in transit to a desired pile drivingsite. The skirt assembly is adapted to seal against ground surface 18when air at superatmospheric pressure is present in space 16 and thebottom surface of the base is either at or within the distance fromground surface 18 which is indicated by dimension 19 in FIG. 2. Distance19 is referred to herein as the maximum stable hover height of theplatform and is the distance between ground surface 18 and the platformbottom surface 17 when air at the appropriate superatmospheric pressure(about one to three pounds per square inch gage pressure) is supplied tospace 16. Preferably, hover height 19 is on the order of 4 to 6 feet. Apair of air blowers 20, such as centrifugal blowers, are mounted to themain deck 21 of base 11, and a suitable motor or diesel engine 22 isprovided in association with each blower for powering the same. Theoutlet opening of each blower is communicated to air cushion space 16 bysuitable ducts (not shown) through the structure of base 11. A turretcrane 23 is mounted to the base deck adjacent slot 12 to facilitate thehandling of piles during the use of pile driver 10.

FIGS. 1 and 2 show pile driver 10 in the process of driving one of aseries of tubular piles 25, each of which has a closed pointed lower end26. The minimum width of slot 12 is defined relative to the largest pileto be driven by the pile driver so that, when skirt assembly 15 is fullyexpanded as a result of air being applied to air cushion space 16 fromblowers 20, the opposing surfaces of the skirt assembly along the slotmake no more than light grazing contact with the surfaces of a piledisposed within the slot.

A vertical framework 27 is mounted on the main deck of base 11 to spanthe inner end of slot 12 (see FIG. 2) and defines a vertical guide trackfor a pile cap member 28. The framework constrains the cap member tomove only vertically up and down relative to the pile driver base.Preferably, the guide portions of the framework 27 are defined by a pairof parallel wide flange beams 29 of suitable size which areinterconnected at their upper ends by a cross-member 30. Framework 27 isstabilized by a strut member 31 connected between the cross-member andmain deck 21 forwardly of the inner end of pile access slot 12.

A selectively operable clamp assembly 32 (see FIG. 2) is mounted to base1 l in association with framework 27 for releasably engaging a pile 25disposed vertically through slot 12 in line with the direction ofmovement of cap member 28. Clamp assembly 32 is provided fortransferring all or a substantial portion of the weight of pile driver10 to a pile in the manner described below. The clamp assembly includesa pair of shoe members 33 which are configured to mate with the exteriorof pile 25 on opposite sides of the pile. Preferably, the surfaces ofthe shoe members which cooperate with the pile carry hardened steelfriction members (not shown) for biting superficially into the materialof the pile to prevent slippage of the shoe members along the pile. Itwill be appreciated that, in the example shown in FIGS. 1 and 2, theshoe members are semi-circularly configured; where a pile of non-tubularconfiguration is used, then the configuration of the shoe members ismodified accordingly.

Each shoe member is mounted by a corresponding double acting ramassembly 34 to a corresponding foundation structure 35 for movementtoward and away from engagement with a pile disposed, as describedabove, through slot 12. Preferably the shoe members are movable parallelto the main deck of the pile driver base. Considering the functionswhich the shoe members, ram assemblies and foundation structures arecalled upon to perform, it is apparent that these elements of piledriver 10 are of substantial strength, and that the foundationstructures are functionally an integral part of the structure of piledriver base 11. Preferably ram assemblies 34 are hydraulic rams whichare operated in response to the operation of a suitable hydraulic powermechanism which is well within the talents of the art and is thereforenot illustrated.

To enable cap member 28 to be raised and lowered within framework 27, awinch 36 is mounted to base main deck 11. Cables 37 extend from thewinch to the cap member and are guided by suitable pulleys 38 locatedadjacent the bottom of track members 29 and by additional pulleys 39mounted to the upper ends of the track members. If desired, appropriateshock absorber mechanisms 40, see FIG. 6, may be coupled between thewinch and the cap member.

Cap member 28 functions as a coupling member between the upper end of apile being driven and a hammer mechanism 41 carried by the cap memberbetween track members 29. The hammer mechanism may be a conventionaldiesel hammer or it may be a Bodine sonic hammer if desired. Preferablycross-member 30 is in yoke form so that the cross-member will notinterfere with the hammer mechanism when the cap memher is elevated tonear the upper ends of the track members.

The driving of a pile by pile driver is commenced by placing the pilevertically through retracted clamp shoes 33 into contact with groundsurface while the pile driver base rests directly upon the ground. Airblowers are operated to supply air at suitable superatmospheric pressureto the space within skirt assembly 15 to cause the base to rise to itshover height 19 above the ground. As the base rises to its hover height,the pile slips downwardly through the retracted shoe members. Eitherbefore or after raising the base to its hover height, cap member 28 ismated to the upper end of the pile. After the pile driver base has beenelevated to its operating hover height, ram assemblies 34 are operatedto securely engage clamp shoes 33 with the pile. The pressure of airwithin air cushion space 16 is reduced to atmospheric pressure, or tosome reduced pressure between atmospheric pressure and the pressureproductive of hover height 19. In this manner, all or a substantialportion of the mass of pile driver 10 is transferred to pile 25, andthis loading of the pile is sufficient to cause the pile to be drivensome distance into the ground.

If the resistance of the ground to penetration by pile is sufficientlylow that the platform moves into direct contact with ground surface 18,then clamp shoes 33 are relaxed from forceful engagement with pile 25,and air is again supplied to air cushion space 26 to again raise theplatform to maximum hover height; the clamp shoes are then againre-engaged with the pile, and the pressure within air cushion space 16is reduced to again cause all or a substantial portion of the weight ofthe pile driver to be transferred to the pile and to cause the pile tofurther penetrate the ground.

If the nature of the ground is such that the pile can be driven to thedesired depth by repeating the foregoing procedures, then theseprocedures are repeateda sufficient number of times to accomplish thedesired pile driving function; in this case the use of hammer assembly41 is not necessary. On the other hand, if pile 25 is to be drivenfurther into the ground than is possible by repeated practice of theload transferring procedures described above, then the pile drivingeffect of hammer assembly 41 is superimposed upon the pile drivingeffects of the above-described procedure. That is, if the maximum depthto which pile 25 can be driven in the ground is say, 30 feet, using onlythe deadweight of pile driver 10, and it is desired to drive the pile toa depth of feet, then the above-described procedure is continued oncethe pile reaches the 30-foot depth in combination with the pile drivingeffects of hammer assembly 41.

During pile driving operations in which hammer assembly 41 is used, theportion of the deadweight of pile driver 10 applied to the pile providesa downwardly acting, high level preload upon the pile. This preloadingof the pile greatly enhances the effectiveness of hammer assembly 41 todrive the pile.

To insure that the deadweight of pile driver 10 is applied vertically topile 25, it is desired that. the center of mass of the pile driver,including all of the equipment carried by the pile driver, be verticallyaligned with the centroid of thearea enclosed by skirt assembly 15.

If the area enclosed by skirt assembly 15 is 940 square feet(corresponding to a base of about 31 feet by 31 feet excluding the slotarea) and the hover air pressure applied to air cushion space 16 is 3psig, then pile driver 10 may weigh up to 500,000 pounds and all or aportion of this mass may be applied in the manner described above topile 25.

Another pile driver 45 is illustrated in FIG. 3 and is similar to piledriver 10 except that pile driver 45 includes a skirt assembly 46 whichis effective to seal against both superatmospheric and subatmosphericpressures in air cushion space 16. Also, pile driver 45 includes ablower 47 coupled by duct 48 to air cushion space 16 to provide partialevacuation of air cushion space 16. The pile driver also includes apressure relief duct 49 through base 11 in combination with a cyclicallyoperable valve 50. While a key slot similar to slot 12 is not shown inFIG. 3, it is understood that pile driver 45 defines such a slot topermit the pile driver to be moved laterally away from a pile whichextends above ground surface 18 after the same has been driven into theground. It will also be understood that while the same is not shown inFIG. 3, pile driver 45 includes blowers, similar to blowers 20, forsupplying air at superatmospheric pressure to air cushion space 16 by asuitable duct, a framework similar to framework 27, and a suitablehammer assembly.

Duct 48 is connected to the section port of blower 47. The blower isoperable to withdraw air from air cushion space 16 and to discharge suchair to atmosphere. Thus, the blower is effective to reduce the pressurein air cushion space 16 to a pressure below atmospheric pressure,assuming that skirt assembly 46 is effective as intended to seal againstground surface 18 when the pressure within air cushion space 16 is lowerthan ambient, i.e. atmospheric pressure.

FIG. 4 is an enlarged perspective view of valve 50 and duct 49. Valve 50includes a drum-like housing 51 which has its axis disposedperpendicular to and in intersection with the axis of duct 49. A pair ofdiametrically opposed ports 52, preferably configured to correspond withthe cross-sectional configuration of duct 49,

are formed through valve housing 51. A plate-like valve member 53 isdisposed within the housing and is carried by a shaft 54 which extendsaxially of the housing from a drive motor 55. The length and width ofthe valve plate is sufficient that it makes slidable sealing contactwith the inner surfaces of housing 51. During one full rotation of shaft54, valve plate 53 cooperates with the inner surfaces of the housing toproduce two cycles in which the valve is changed substantiallyharmonically from a full-open state (in which the valve member isdisposed in the plane of the axis of duct 49) and a closed state (inwhich the valve member is disposed perpendicular to the axis of duct49).

The operational procedures useful with pile driver 45 are similar to theprocedures described above for operation of pile driver 10, except thatthe pressure in air cushion space 16 is reduced to a pressure belowambient pressure after. the platform has been raised to its maximumstable hover height and clamped to a pile to be driven. Therefore, inpile driver 45 a downward preload force greater than the weight of thepile driver and its associated equipment is applicable to a pile. Forexample, if the deadweight of the pile driver and its associatedequipment is 500,000 pounds and this mass can be supported at full hoverheight by cushion air at 3 psig, and if the pressure produced in aircushion space 16 by operation of blower 47 is 1 pound per square inchless than ambient pressure, then the total downward force capable ofbeing applied to a pile by pile driver 45 is 666,667 pounds, i.e.500,000 pounds plus one-third (500,000 pounds).

It is believed that a pile can be driven considerably faster than hasheretofore been possible if the pile is subjected to a static downwardbias force on which cyclic downward forces are superimposed. This isprecisely the type of action produced by the operation of pile driver 10when hammer assembly 41 is used. Pile driver 45, however, is capable ofproducing all of the pile driving effects of pile driver 10 with theadditional effect of a downwardly acting cyclic driving load separatefrom those cyclic forces applied to the pile hammer assembly 41. Theseadditional downwardly acting pile driving loads are produced when valve50 is operated in conjunction with pressure reducing blower 47.

That is, assuming the exemplary dimensions and characteristics of driver45 mentioned above, it is apparent that of the 666,667 lb. load capableof being applied by the pile driver to pile 25 when the air pressure inair cushion space 16 is l lb. psi less than ambient pressure, 166,667pounds of that load is attributable to the pressure difference existingacross skirt assembly 46. This pressure difference can exist only whenvalve 50 is in its closed state within duct 49. However, this pressuredifference can be eliminated or significantly reduced by opening valve50. Therefore, when valve 50 is operated cyclically simultaneously withthe operation of blower 45, the 166,667 lb. increment of the total loadcapable of being applied by the pile driver to the pile is cyclicallyvariable, with the 500,000 lb. load associated with the dead weight perse. of the pile driver being constantly applied to the pile. The drivingforce variation associated with the pressure differential existingacross the skirt assembly 46 may be found to be sufficient, inconjunction with the steady state driving force attributable to the deadweight of the pile driver, to drive pile 25 to its desired depth in theground. If not, then hammer assembly 41 may be operated in conjunctionwith the cyclic driving force associated with operation of valve 50.

' Valve 50 may be operated to open and close with a frequency whichcorresponds to that of hammer assembly 41, or the operative frequenciesof the hammer assembly and valve 50 may be different, as desired. Wherethe valve and hammer assembly frequencies are the same, they may beoperated either in phase or out of phase with each other. If theoperative frequencies of the hammer assembly and the valve aredifferent, then the operational frequency of the valve may be anintegral number of times greater than that of the hammer assembly, or itmay be a non-integral number of times different from that of the hammerassembly. The precise relationship between the operative frequencies andthe phase of hammer assembly 41 relative to valve 50 will be determinedby the mechanics of the soil into which the pile is being driven and howthese factors may best be combined with each other to achieve themaximum rate of penetration by the pile.

FIG. 5 is a fragmentary cross-sectional view of a portion to anotherpile driver 60 according to this invention. Pile driver 60 is similar topile driver 45 except that elements 47, 48, 49 and 50 of pile driver 45are replaced by the blower and ducting arrangement shown in FIG. 5. Thatis, in pile driver 60, the evacuating blower 47 of pile driver 45 isreplaced by a pressurizing and evacuating blower 61 having a suctionport 62 and a discharge 63. The suction port of blower 61 is selectivelyconnectible either to atmosphere or to air cushion space 16 by a valve64 and by ducts 65 and 66, respectively. The blower discharge isselectively connectible either to atmosphere or to air cushion space 16by a valve 67 associated with ducts 68 and 69, respectively. Valves 64and 67 are operated either in tandem or separately, as desired, by asuitable control mechanism 70. Preferably, pressurizing and evacuatingblower 61 is provided in addition to pressurizing blowers 20 which arenot operative to affect the pressure in air cushion space 16 after thebase of pile driver 60 has been clamped to a pile in the mannerdescribed above.

Assume that blower 61 is operative to produce an air cushion spacepressure of 1 pound per square inch less than ambient pressure when thesuction of the blower is connected to the air cushion space via valve 64and duct 66. Assume also that blower 61 is operative to produce in aircushion space 16 a pressure which is 1 pound per square inch greaterthan ambient pressure when the blower discharge is applied to the aircushion space via valve 67 and duct 69. Under these circumstances, it isapparent that blower 61 is effective, in response to the appropriatecontrol of valves 64 and 67, to produce a downwardly effective cyclicforce variation (attributable to pressure differential across the skirtassembly sealing space 16) on a pile, and that the magnitude of thisvariable force is twice the magnitude of the cyclic force capable ofbeing applied to the pile by pile driver 45, all other things beingequal between the two pile drivers. That is, after the pile driver hasbeen securely clamped to a pile following elevation of the pile driverbase above ground surface 18, and after blowers 20 have either been shutdown or valved to discharge to atomoshere, blower 61 can be operated toevacuate air cushion space 16 so that the effective force applied by thepile driver (both dead weight and pressure differential force) is666,667 pounds. On the other hand, when the discharge of blower 61 isapplied to air cushion space 16 following clamping of the pile driverbase to the pile, the effective downward force applied by the piledriver to the pile is 333,333 pounds; in this case, one-third of the500,000 pound deadweight of the pile driver is supported by the air inspace 16 and the remainder is carried by the pile itself. Thus, thepressure-related cyclic force applied by the pile driver to the pile, asvalves 64 and 67 are cycled between the conditions shown in solid linesand in broken lines in FIG. 5, varies between a maximum of 666,667pounds and a minimum of 333,333 pounds, at least 333,333 pounds alwaysbeing applied to the pile by the pile driver whether or not hammerassembly 41 is operated.

Preferably control mechanism is arranged to operate valves 64 and 67 intandem in such manner that, when valve 64 is disposed to close duct 55and to place duct 66 in communication with the suction port of blower61, valve 67 is disposed to close duct 69 and to couple the discharge ofthe blower to atmosphere via duct 58. Conversely, when valve 64 isdisposed to close duct 66 and to couple the suction port of the blowerto atmosphere via duct 65, valve 67 is disposed to close duct 68 and tocouple the blower discharge to air cushion space 16 via duct 69.

It has been found that the maximum hover height capable of beingattained by a given air cushion vehicle is a combination of many things,including the deadweight of the vehicle, the effective area enclosed bythe air cushion sealing skirts, and the pressure of air applied to theair cushion space within the skirt assembly. Inasmuch as air iscompressible, the volumetric capacity of the pressurizing blowers orcompressors, as well as the pressure capable of being developed by thesemechanisms, is also relevant. The volumetric capacity of thepressurizing mechanisms for the vehicle should exceed the leakageexisting around the skirt assembly during air cushion mode operation ofthe vehicle. In this context, when the air cushion pressurizingmechanism is operated at a rate peculiar to the massand geometry of thevehicle, the vehicle will rise to its maximum stable hover height abovean adjacent ground surface. If the air pressurization mechanism isoperated so that its effective volumetric capacity equals the rate atwhich air leaks out of the air cushion space past or through the aircushion skirt assembly, the maximum hover height will be maintained in astable manner. However, when the pressurization mechanism is operated ata pressure and effective volumetric capacity which is significantlygreater than that associated with the maximum stable hover height, thevehicle will oscillate vertically at a characteristic frequency. Duringsuch oscillation, the maximum height of the air cushion vehicle abovethe adjacent ground surface is the maximum stable height of the vehicleor a distance somewhat greater than the maximum stable hover height. Thevertical distance through which the vehicle moves during suchoscillation is less than the maximum stable hover height of the vehicle.

The vertical oscillation of an air cushion vehicle due to overpoweringthe air cushion support mechanism is believed to be induced as theoversupply of air at sup'eratmospheric pressure is relieved from the aircushion space by popping atmosphere to around the lower portions of theair cushion skirt assembly. As this occurs, the pressure in the aircushion space is momentarily reduced below the air pressure productiveof the maximum stable hover height. Accordingly, the vehicle tends todrop toward the adjacent ground surface, but in such movement the skirtassembly is brought into effective sealing contact with the ground. Asthis occurs, the downward movement of the vehicle is arrested by thecompression of the air trapped within the air cushion space. Continuedoperation of the air pressurizing mechanism again raises the vehicle tothe maximum stable hover height, or somewhere beyond, until theoverpressure in the air cushion space is reestablished and theoverpressure is again relieved by the popping phenomenon.

Pile driver 75, see FIG. 6, is arranged to be operated in theabove-mentioned vertical oscillatory mode during the process of drivingpile 25, and to apply at least a portion of the kinetic and potentialenergy of the platform attributable to downward oscillatory movement tothe pile as a dirving input to the pile. To the extent that pile driver75 includes structural features like those described above for piledriver 10, they are shown in FIG. 6 by the use of appropriate characternumbers.

Pile driver 75 includes a clamp assembly 76 which differs from clampassembly 32 of pile driver 10 in that it is not carried directly by thestructure of base 11. The

clamp assembly includes a pair of clamp shoes 77 which are movable intoand out of secure mating contact with the external configuration of pile25, and which preferably carries hardened teeth or the like forsuperficially biting into the pile to prevent slippage of the shoesalong the pile. Suitable ram assemblies (not shown) are connectedbetween shoes 77 to move them relative to each other into and out ofmating engagement with a pile. A flexible connection 78 for supplyingsuitable control and power fluid to the clamp assembly is connectedbetween it and base platform 11.

A heavy annular loading member 79 is mounted to base 11 and is locatedabove the upper extent of clamp assembly 76. The loading member isdisposed concentric, to the line along which pile 25'is disposed duringpile driving operation of pile driver 75. The loading member may bemounted either directly to framework 27 by supports 80 (see FIG. 6) orit may be carried by suitable supports 81 connected to base main deck 21(see FIG. 7). The distance between the underside of loading member 79and main deck 21 is greater than the vertical extent of clamp assembly76 and preferably is greater than the sum of a) the vertical extent ofthe clamp assembly and b) the range of vertical movement of the baserelative to ground surface 18 during vertical oscillatory movement ofthe pile driver in the manner described above.

Clamp assembly 76 is coupled to pile driver 75 for movement vertically,i.e., upwardly, along a pile when the clamping shoes of the clampassembly are relaxed from intimate mating engagement with the pile. Asshown in FIG. 7, at least a pair of pneumatic ram assemblies 82 (onlyone of which is shown) are coupled between loading member 79 and theouter extent of the clamp assembly. Operating air is supplied to the ramassemblies by suitable connections (not shown). Preferably ramassemblies 82 are a portion of the clamp assembly control and operatingmechanism of which flexible connections 78 are a part.

Pile driver 75 may be operated to at least partially drive a pile byapplying all of the deadweight of the pile driver to the pile. The piledriver is raised to its maximum stable hover height above ground surface18, clamp assembly 76 is moved into abutment with the lower portion ofloading member 79 while the clamp shoes are relaxed, the clamp assemblyis operated to securely grip the pile, and then the supply of hover airto air cushion space 16 is discontinued. This process is repeated untilthe pile can no longer be driven into the ground. Thereafter, the pileis further driven by operating hammer assembly 41 and by operation ofthe pile driver in the vertical oscillatory mode described above.

For oscillatory operation of pile driver 75, the base is disposed at itsmaximum stable hover height above ground surface 18; clamp assembly 76is secured to the pile at a location in which the upper surface of theclamp assembly is spaced from the lower portion of loading member 79 bya distance which is less than, but more than half of, the range ofvertical oscillatory movement of the pile driver. Blowers 20 are thenoperated to oversupply air to air cushion space 16. As the base movesthrough its first downward oscillatory excursion, loading member engagesclamp assembly 76 while the pile driver is still moving downward, and inthis way a substantial portion of the kinetic energy of the pile driver,and its residual potential energy, are transferred to the pile via theclamping assembly.

Once the pile has been driven a distance equal to the verticaloscillatory movement of the pile driver, loading member 79 isineffective to further supply loads to pile 25. At this point, clampingassembly 76 is relaxed on the pile and ram assemblies 82 are operated toraise the clamp assembly along the pile to reestablish the initialspacing of the clamp assembly below loading member 79. Preferably thisrepositioning of the clamp assembly on pile is done during continuedoscillation of pile driver 75 and during continued operation of hammerassembly 41 so that driving of the pile is not interrupted.

Because base platform 11 of pile driver 75 may not be stationary ashammer assembly 41 is operated, it is desirable that cap member 28 floatwithin framework 27. It may be desirable to install shock absorbermechanisms 40 in cables 37 which suspend the cap member from the upperend of the framework.

To impart maximum operational flexibility and versatility to pile driver75, the pile driver may include a pressurizing and evacuating systemlike or similar to that shown in FIG. 5. Such a pile driver is capableof applying both static, pressure-related cyclic and oscillatory drivingloads to a pile onto which conventional pile driving loads, such as areproduced by operation of hammer assembly 41, may be superimposed.

In pile driver 45 (see FIG. 3) air cushion space 16 is bounded by skirtassembly. 46 which is effective to seal against the ground surface 18when the pressure within the air cushion space is either above or belowambient pressure, i.e., atmospheric pressure in the usual case. Thestructure of skirt assembly 46 is shown in greater detail in FIGS. 8, 9and 10, which clearly illustrate that, in the presently preferredpractice of this invention, pile driver base platform 11 resembles aflat-bottom barge having sloped bilges. That is, the base has a gunwale85 at which the flat main deck of the base intersects vertical sidewalls 86. The side walls intersect the upper edge of a chine surface 87which extends obliquely between the bottom and side surfaces of thebase.

Skirt assembly 46 is composed of inner and outer flexible air-impervioussheets 88 and 89, respectively. Sheets 88 and 89 preferably are definedby a fabric which has been impregnated with a suitable elastomer. Innersheet 88 has its upper margin connected to base 11 at about theintersection of bottom surface 17 and chine surface 87. Outer sheet 89has its upper margin connected to the base at about the intersection ofchine surface 87 with side wall surface 86. The lower margins of theinner and outer sheets are interconnected at the bottom of the skirtassembly.

The desired configuration of the skirt assembly, during sealing ofsuperatmospheric pressure in air cushion space 16, is established by aplurality of flexible inelastic straps or tapes, a set of which areinterconnected between base 11 and outer sheet 89 at each of a pluralityof locations spaced around the periphery of the base. Each set of tapesinclude a tape 90 which is connected at one end to the base between theinner and outer sheets adjacent the connection of the inner sheet to thebase; this tape is connected at its other end to the outer sheetadjacent its connection to the lower margin of the inner sheet. Anothertape 91 is disposed between the inner and outer sheets, and has itsupper end connected to the base adjacent the upper margin of the outersheet and its lower end connected to the outer sheet adjacent theinterconnection of the outer and inner sheets. Additional tapes 92 aredisposed between the inner and outer sheets and have their inner endsconnected to the base at spaced locations along chine surface 87, andtheir outer ends are connected to the outer sheet at spaced locationsalong the extent of the outer sheet between its upper and lower margins.

In skirt assembly 46, outer sheet 89 is effective at and adjacent itslower margin to seal against ground surface 18 when the air pressure inair cushion space 16 is above ambient pressure. Inner sheet 88 iseffective at and adjacent its lower margin to seal against groundsurface 18 when the pressure in air cushion space 16 is below ambientpressure. The surface of the sheet which faces toward air cushion space16 is referred to, for the sake of convenience, as the inner surface ofthe sheet, whereas the surface of the sheet which faces away from theair cushion space is referred to as the outer surface of the sheet.

As shown best in FIG. 10 (which is included for the purposes ofillustration and which does not represent a normal operative state ofthe skirt assembly), a plurality of ports 93 are formed through theinner sheet at spaced locations along the extent of the sheet about theperiphery of base 1 1. Ports 93 are located adjacent, but not at, thelocation at which the inner sheet is connected to the lower margin ofthe outer sheet. Similarly, a plurality of ports 94 are formed throughthe lower portions of the outer sheet adjacent, but not at, theinterconnection of the outer sheet to the inner sheet. A check valve iscarried by inner sheet 88 in association with each of ports 93 to permitair to pass through the port only from the inner to the outer surface ofthe sheet. A similar check valve 95 is carried by the outer sheet inassociation with each of ports 94 to permit air to flow through ports 94only in the direction processing from the outer surface to the innersurface of the outer sheet. A suitable check valve may be defined of aflap of air impervious material mounted to the sheet so that it mayoverlay the adjacent port. The flaps are secured to the outer surface ofthe inner sheet, and to the inner surface of the outer sheet.

FIG. 8 shows skirt assembly 46 sealing against super atmosphericpressure in air cushion space 16; the air pressure in the air cushionspace is presented to the inner face of outer sheet 89 via inner sheetports 93. To facilitate effective presentation of the pressure in theair cushion space to the outer sheet, the inner sheet is self-retracted,as shown in FIG. 8, by self-retraction devices carried by the innersheet and described below with reference to FIG. 14. On the other hand,when the air pressure within air cushion space 16 is less than ambientpressure, the appropriate seal of the air cushion space is provided byinner sheet 88. Ambient air pressure is presented to the outer face ofinner sheet 88 via outer sheet ports 94, and outer sheet 89 isselfretracted (see FIG. 9).

The self-retraction of the inner and outer sheets of skirt assembly 46is provided by elastic retraction straps 96 secured to the sheets atspaced locations around the periphery of base 11. Each retraction strapis disposed vertically in the skirt assembly and is secured at itsopposite ends to the respective skirt sheet, as by stitching 97.Intermediate its ends, the strap is guided through loops formed on theadjacent surface of the skirt sheet by a plurality of transverselydisposed flexible tapes secured, as by stitching, at its opposite endsto the sheet on either side of the retraction strap. When the skirtsheet is in its operative position, the retraction straps are extended.The elastic stiffness of the several retraction straps associated witheach skirt sheet is sufficiently low that the skirt sheet can assume thedesired configuration when the appropriate pressure differential existsacross the sheet.

Skirt assembly 46 has an external configuration which resembles aconventional air cushion skirt assembly when the pressure within aircushion space 16 is greater than ambient pressure. Thus, pile driver 45can be moved on a cushion of air from place to place over the groundsurface.

Another air cushion skirt assembly 100, suitable for use in pile driver45, is shown in FIGS. 11, 12' and 13. Skirt 100 includes a principalsheet 101 which is fabricated of a flexible, air impervious material andwhich is connected to base 11 at its upper extent adjacent theintersection of chine surface 87 and side surface 86. A plurality ofpositioning partition webs 102 are provided at regularly spaced stationsalong the extent of the skirt assembly around base 11. Each partitionweb is connected to the base along chine surface 87 and also to theinner surface 103 of sheet 101. Sheet 101, adjacent its lower margin, isdisposed at an acute angle to ground surface 18.

Skirt assembly 100 also includes a sealing assembly 105 which extendsalong the length of the skirt and is carried by the lower portion of theprincipal sheet. The sealing assembly defines an inflatable innerchamber 106 which, when inflated, is of generally triangularconfiguration. The sealing assembly is fabricated of air imperviousflexible material and includes a lower sheet 107 adapted to be engageddirectly with ground surface 18. An outer sheet 108 and an inner sheet109 are connected at their lower edges to the opposite edges of sheet107; the upper edges of the inner and outer sheets are interconnected toeach other and to principal sheet 101. If desired, sheet 109 may beeliminated from sealing assembly 105 by connection of the upper marginof sheet 108 directly to principal sheet 101 at an intermediate locationalong the vertical extent of the principal sheet, and by connection ofsheet 107 at its inner edge to the lower margin of the principal sheet.

Sealing assembly chamber 106 is connected at appropriate locations alongthe skirt via suitable flexible ducts 111, to a compressor 110 disposedwithin base 11; see FIG. 12.

FIG. 11 illustrates skirt assembly 100 sealing against superatmosphericpressure within air cushion space 16. FIG. 12 shows the skirt assemblysealing againstsubatmospheric pressure within the air cushion space. Theseal against superatmospheric pressure is provided by inner sheet 109being forced outwardly and downwardly relative to base 11. Aparticularly effective positive seal is obtained by pressurizing chamber106 so that the outward and downward bias applied to sheet 109 bysuper-atmospheric pressure within space 16 urges sheet 107 into sealingcontact with ground surface 18 over an extended area circumferentiallyof base 1 1.

On the other hand, during negative sealing conditions i.e. when thepressure in air cushion space 16 is less than atmospheric pressure,sheets 107 and 108 of sealing assembly 105 are effective to produce thedesired seal against the leakage of air into space 16. To provide thedesired negative seal, chamber 106 is pressurized. Air at atmosphericpressure is effective on the outer surface of sheet 108 to bias theentire sealing assembly into engagement with ground surface 18.

Sealing assembly 105 is used to provide the desired positive andnegative seals when base 11 is at a desired operational location and isnot being moved horizon tally across ground surface 18. To facilitatemovement of base 11 from one pile driving site to another, sealingassembly 105 is retracted as shown in FIG. 13. At spaced locations alongthe extent of the skirt assembly, corresponding ones of a plurality ofcables 113 are connected to the sealing assembly at the connectionbetween sheets 107 and 108. Cables 113 are guided by suitable pulleys114 to suitable winches on the base. When air at superatmosphericpressure is present in air cushion space 16, a positive seal againstground surface 18 is provided by the lower portions of principal sheet101, by sheet 109, and by the inner margins of sheet 107, even when thesealing assembly has been retracted. Retraction of the sealing assemblyis achieved by pulling'in cables 13 so that the skirt assembly mayfunction like a conventional skirt.

Skirt assembly is arranged so that sheet 109 of sealing assembly iseither directly below or slightly outboard of chine surface 87 duringuse of the skirt assembly. This relative positioning of the chinesurface and sheet 109 make it possible for base 11 to directly engageground surface 18, as when subatmospheric air pressure in air cushionspace 16 is used to apply an increased static load to a pile for initialdriving of the pile, without damaging pinching of the skirt assembly orthe sealing assembly by the base.

It will be appreciated that both skirt assemblies 46 and 100 may be usedto support base 11 over water for marine usages of the pile driversdescribed above. The negative differential sealing properties of skirtassemblies 46 and 100 have utility in applications other than the piledrivers described above. For example, a negative sealing skirt assembly124 is mounted about the periphery of a crawler tractor 120, see FIG.15, for increasing the effective weight of the vehicle, to therebyincrease the effective drawbar pull, without significantly increasingthe actual weight of the vehicle. A mounting structure 121 is added tothe vehicle to define a deck 122 around the vehicle above the endlessbelt crawler mechanism 123 on which the tractor body is supported. Thesupport structure preferably extends sufficiently far outwardly,forwardly, and rearwardly on the tractor body to prevent anyinterference by the skirt assembly 124 with the vehicle propulsionmechanism. The support structure has a downwardly extending peripheralflange 125 to which the skirt is connected. An evacuating blower 126 iscarried by the mounting structure and has its suction port connected tothe interior of the skirt. The skirt assembly includes an inflatablesealing and wear tube 127 around its lower periphery for maintainingcontact with an uneven ground surface. Operation of blower 126 increasesthe apparent deadweight of the vehicle, and thereby increases thepulling power of the tractor at drawbar 128.

A positive and negative sealing skirt assembly 130 is a component of aworkpiece transporting and positioning platform 131 (FIG. 16) for use ina large machine shop or the like. Platform 131 includes a base 132 whichcarries a plurality of support blocks 134 on its lower surface 135within an air cushion space 136 bounded by skirt assembly 131. The baseis movable across a desired floor 137 on a cushion of air atsuperatmospheric pressure generated within the air cushion space byoperation of a pressurizing blower 138 mounted to the base and havingits discharge connected to the air cushion space. Subatmosphericpressure may be generated in air cushion space 136 by operation of anevacuating blower 139 carried by the base and having its suction portcoupled to the air cushion space by a suitable duct 140. A largeworkpiece141 is held in position on the upper surface of the base by aplurality of conventional machinists dog assemblies 142 engaged inappropriate grooves or slots in the upper surface of the base.

If a plurality of holes are to be drilled vertically in the upperportion of workpiece 141 by a large vertical boring mill, platform 131is moved on a cushion of air across'floor 137 and onto the rotary tableof the boring mill while pressurizing blower 138 is operated. Duringsuch movement of the platform, base 132 is elevated sufficiently thatsupport blocks 134 are raised above the floor. So long as the base issupported on a cushion of air, it is a simple matter to align theplatform on the boring mill rotary table without the use of hoists orthe like. Once the platform is properly positioned, air cushion supportof the base is discontinued and the platform is settled onto the boringmill table for support thereon by blocks 134. Evacuating blower 139 isthen operated and subatmospheric pressure is generated in the aircushion space. In effect, base 132 and skirt assembly 131 function as alarge suction cup to securely hold the platform in the desired positionfor machining of the workpiece. After the desired holes have beendrilled, it is a simple matter to move the workpiece to anothermachining station.

Workers skilled in the art to which this invention pertains will readilyappreciate that the foregoing embodiments of apparatus and proceduresaccording to this invention have been presented by way of example ratherthan as an exhaustive delineation of all forms which this invention maytake. Accordingly, it will be understood that the procedures andstructures described above may be modified or altered without departingfrom the scope and spirit of this invention while still having thebenefit of the advantages which this invention has provided. Therefore,the foregoing description of presently preferred embodiments andapplications of this invention should not be considered as limiting thescope of the invention.

What is claimed is:

1. A pile driver comprising:

a. a base,

b. selectively operable means operable independently of any piles andthe like previously driven for supporting the base in an elevatedposition above ground and the like,

c. means for disposing a pile substantially vertically of the base inengagement with ground adjacent the base into which the pile is to bedriven, and

(1. means operable in the elevated position of the base for transferringat least a substantial portion of the weight of the base to a piledisposed vertically of the base.

2. A pile driver according to claim 1 including impact means carried bythe base and engageable with the upper end of a pile disposed verticallyof the base.

3. A pile driver according to claim 1 including load receiving meansattachable to a pile to be secure from movement longitudinally of thepile, wherein the selectively operable means is operable to cause thebase to move cyclically substantially up and down within a range lessthan the distance between the base and ground in the elevated positionof the base, and means carried by the base for cooperating with the loadreceiving means to transfer to the load receiving means at least aportion of the momentum of the base due to downward cyclic movementthereof.

4. A pile driver according to claim 3 including means cooperatingbetween the base and the load receiving means for adjusting the positionof the load receiving means along the pile.

5. A pile driver according to claim 4 wherein the position adjustingmeans is operable for maintaining the load receiving means at a locationon the pile which is a selected distance from a reference location onthe base when the base is at a predetermined position within its rangeof cyclic movement.

6. A pile driver according to claim 5 wherein the position adjustingmeans includes means for clamping the load receiving means to the pile,and means for operating the clamping means in synchronism to cyclicvertical motion of the base.

7.A pile driver according to claim 1 wherein the base defines an openingvertically therethrough in vertical alignment with the center of mass ofthe base, and wherein the means for disposing a pile is arranged todispose the pile through said opening.

8. A pile driver according to claim 7 wherein said opening extends toand opens through a margin of the base.

9. A pile driver according to claim 7 wherein the selectively operablemeans includes a flexible skirt assembly carried by the basesubstantially peripherally thereof for enclosing a space between thebase and ground and the like, and means for supplying air atsuperatmospheric pressure to the space.

10. A pile driver according to claim 9 wherein the skirt assembly isarranged to effectively enclose said space in the presence of air atsubatmospheric pressure within the space, and means for evacuating airfrom the space.

11. A pile driver according to claim 10 including an air blower commonto the air supplying means and the evacuating means.

12. A method for driving a pile and the like comprising the steps of:

a. providing an elevatable base,

b. disposing a pile to be driven substantially vertically through thebase with the lower end of the pile in engagement with ground into whichthe pile is to be driven,

c. elevating the base from a lower position thereof relative to theground and the pile independently of the pile and any other pilespreviously driven, and

d. applying to the pile at least a portion of the weight of the baseincluding coupling the base to the pile at a position of the base abovethe lower position thereof.

13. The pile driving method according to claim 12 wherein the base iscoupled to the pile when the base is at its elevated position, andfurther including the step of withdrawing at least a substantial portionof the support of the base following coupling of the base to the pile.

14. A pile driver comprising: a. a base,

b. selectively operable means operable for supporting the base in anelevated position above ground and the like,

c. means for disposing a pile substantially vertically of the base inengagement with ground adjacent the base into which the pile is to bedriven, and

d. means operable in the elevated position of the base for transferringsubstantially the entire weight of the base to a pile disposedvertically of the base.

15. A pile driver according to claim 14 wherein the weight transferringmeans includes clamp means carried by the base and engageable with apile.

16. A pile driver according to claim 15 including means coupled to thebase and operable in the elevated position of the base for enclosing aspace between the base and ground and the like below the base, and meansfor generating subatmospheric pressure within the space.

17. A pile driver according to claim 16 including means for cyclicallyaltering the pressure within the space relative to atmospheric pressure.

18. A pile driver according to claim 14 including cyclically operableimpact means carried by the base for applying downward impact forces toa pile disposed vertically of the platform.

19. A pile driver according to claim 18 wherein the impact meanscomprises a sonic hammer.

20. A pile driver according to claim 18 wherein the impact meanscomprises a diesel hammer.

21. A method for driving a pile and the like comprising the steps of:

a. providing an elevatable base, b. disposing a pile to be drivensubstantially vertically through the base with the lower end of the pilein engagement with ground into which the pile is to be driven, a I c.elevating the base from a lowered position thereof relative to theground and the pile by l. enclosing a space between the base and groundbelow the base with a flexible skirt assembly coupled to the base, and

2. supplying air at superatmospheric pressure to the space,

d. coupling the base in the elevated position thereof to the pile, and

e. applying to the pile at least a portion of the weight of the base bywithdrawing at least a substantial portion of the support of the basefollowing coupling of the base to the pile by discontinuing the supplyof air at superatmospheric pressure to the space.

22. The method according to claim 21 including withdrawing air from thespace following discontinuing the supply of air to the space.

23. The method according to claim 21 including supplying air to thespace at a s'uperatmospheric pressure in excess of the pressurecorresponding to the maximum stable elevated position of air cushionsupport of the base above ground, thereby to cause the base to heavecyclically within a range which is less than the maximum stable elevatedheight of the base.

24. The method according to claim 23 including applying to a pile atleast a portion of the energy of the base attributable to said cyclicheaving motion of the base.

25. A pile driver comprising:

a. a base,

b. selectively operable means operable for supporting the base in anelevated position above ground and the like, said means comprising aircushion means for supporting the base on a quantity of air atsuperatmospheric pressure,

c. means for disposing a pile substantially vertically of the base inengagement with ground adjacent the base into which the pile is to bedriven, and

d. means operable in the elevated position of the base for transferringat least a substantial portion of the weight of the base to a piledisposed vertically of the base.

26. A pile driver according to claim 25 wherein the air cushion means isoperable to cause the base to move cyclically substantially verticallywithin a range of movement in which, at the lower limit of said range,the base is disposed above ground and the like and is supported, in theabsence of other support, upon a quantity of air at superatmosphericpressure, and wherein the weight transferring means includes means fortransferring to a pile at least a portion of the momentum of the basearising from downward movement of the base within said range.

27. A method for driving a pile and the like comprising the steps of:

a. providing an elevatable base,

b. disposing a pile to be driven substantially vertically through thebase with the lower end of the pile in engagement with ground into whichthe pile is to be driven,

c. elevating the base from a lowered position thereof relative to theground and the pile,

d. applying to the pile at least a portion of the weight of the baseincluding coupling the base to the pile at a position of the base abovethe lowered position thereof, and

e. applying impact force to the upper end of the pile followingapplication of at least a portion of the weight of the base to the pile.

28. Apparatus for penetrating a selected elongate member into an earthformation comprising a platform, driving means carried by the platformoperable upon a substantially vertically disposed selected elongatemember located adjacent the platform to urge the member to penetrate anearth formation below the platform, skirt means carried by the platformoperable in combination with ground and the like below the platform forenclosing a space below the platform, means communicating with the spaceoperable for generating subambient pressure within the space thereby toapply to the platform a downward force, and means cooperable between theplatform and the member for transferring a substantial portion of saidforce to the member.

29. Apparatus according to claim 28 wherein the elongate member is apile.

1. A pile driver comprising: a. a base, b. selectively operable meansoperable independently of any piles and the like previously driven forsupporting the base in an elevated position above ground and the like,c. means for disposing a pile substantially vertically of the base inengagement with ground adjacent the base into which the pile is to bedriven, and d. means operable in the elevated position of the base fortransferring at least a substantial portion of the weight of the base toa pile disposed vertically of the base.
 2. A pile driver according toclaim 1 including impact means carried by the base and engageable withthe upper end of a pile disposed vertically of the base.
 2. supplyingair at superatmospheric pressure to the space, d. coupling the base inthe elevated position thereof to the pile, and e. applying to the pileat least a portion of the weight of the base by withdrawing at least asubstantial portion of the support of the base following coupling of thebase to the pile by discontinuing the supply of air at superatmosphericpressure to the space.
 3. A pile driver according to claim 1 includingload receiving means attachable to a pile to be secure from movementlongitudinally of the pile, wherein the selectively operable means isoperable to cause the base to move cyclically substantially up and downwithin a range less than the distance between the base and ground in theelevated position of the base, and means carried by the base forcooperating with the load receiving means to transfer to the loadreceiving means at least a portion of the momentum of the base due todownward cyclic movement thereof.
 4. A pile driver according to claim 3including means cooperating between the base and the load receivingmeans for adjusting the position of the load receiving means along thepile.
 5. A pile driver according to claim 4 wherein the positionadjusting means is operable for maintaining the load receiving means ata location on the pile which is a selected distance from a referencelocation on the base when the base is at a predetermined position withinits range of cyclic movement.
 6. A pile driver according to claim 5wherein the position adjusting means includes means for clamping theload receiving means to the pile, and means for operating the clampingmeans in synchronism to cyclic vertical motion of the base.
 7. A piledriver according to claim 1 wherein the base defines an openingvertically therethrough in vertical alignment with the center of mass ofthe base, and wherein the means for disposing a pile is arranged todispose the pile through said opening.
 8. A pile driver according toclaim 7 wherein said opening extends to and opens through a margin ofthe base.
 9. A pile driver according to claim 7 wherein the selectivelyoperable means includes a flexible skirt assembly carried by the basesubstantially peripherally thereof for enclosing a space between thebase and ground and the like, and means for supplying air atsuperatmospheric pressure to the space.
 10. A pile driver according toclaim 9 wherein the skirt assembly is arranged to effectively enclosesaid space in the presence of air at subatmospheric pressure within thespace, and means for evacuating air from the space.
 11. A pile driveraccording to claim 10 including an air blower common to the airsupplying means and the evacuating means.
 12. A method for driving apile and the like comprising the steps of: a. providing an elevatablebase, b. disposing a pile to be driven substantially vertically throughthe base with the lower end of the pile in engagement with ground intowhich the pile is to be driven, c. elevating the base from a lowerposition thereof relative to the ground and the pile independently ofthe pile and any other piles previously driven, and d. applying to thepile at least a portion of the weight of the base including coupling thebase to the pile at a position of the base above the lower positionthereof.
 13. The pile driving method according to claim 12 wherein thebase is coupled to the pile when the base is at its elevated position,and further including the step of withdrawing at least a substantialportion of the support of the base following coupling of the base to thepile.
 14. A pile driver comprising: a. a base, b. selectively operablemeans operable for supporting the base in an elevated position aboveground and the like, c. means for disposing a pile substantiallyvertically of the base in engagement with ground adjacent the base intowhich the pile is to be driven, and d. means operable in the elevatedposition of the base for transferring substantially the entire weight ofthe base to a pile disposed vertically of the base.
 15. A pile driveraccording to claim 14 wherein the weight transferring means includesclamp means carried by the base and engageable with a pile.
 16. A piledriver according to claim 15 including means coupled to the base andoperable in the elevated position of the base for enclosing a spacebetween the base and ground and the like below the base, and means forgenerating subatmospheric pressure within the space.
 17. A pile driveraccording to claim 16 including means for cyclically altering thepressure within the space relative to atmospheric pressure.
 18. A piledriver according to claim 14 including cyclically operable impact meanscarried by the base for applying downward impact forces to a piledisposed vertically of the platform.
 19. A pile driver according toclaim 18 wherein the impact means comprises a sonic hammer.
 20. A piledriver according to claim 18 wherein the impact means comprises a dieselhammer.
 21. A method for driving a pile and the like comprising thesteps of: a. providing an elevatable base, b. disposing a pile to bedriven substantially vertically through the base with the lower end ofthe pile in engagement with ground into which the pile is to be driven,c. elevating the base from a lowered position thereof relative to theground and the pile by
 22. The method according to claim 21 includingwithdrawing air from the space following discontinuing the supply of airto the space.
 23. The method according to claim 21 including supplyingair to the space at a superatmospheric pressure in excess of thepressure corresponding to the maximum stable elevated position of aircushion support of the base above ground, thereby to cause the base toheave cyclically within a range which is less than the maximum stableelevated height of the base.
 24. The method according to claim 23including applying to a pile at least a portion of the energy of thebase attributable to said cyclic heaving motion of the base.
 25. A piledriver comprising: a. a base, b. selectively operable means operabLe forsupporting the base in an elevated position above ground and the like,said means comprising air cushion means for supporting the base on aquantity of air at superatmospheric pressure, c. means for disposing apile substantially vertically of the base in engagement with groundadjacent the base into which the pile is to be driven, and d. meansoperable in the elevated position of the base for transferring at leasta substantial portion of the weight of the base to a pile disposedvertically of the base.
 26. A pile driver according to claim 25 whereinthe air cushion means is operable to cause the base to move cyclicallysubstantially vertically within a range of movement in which, at thelower limit of said range, the base is disposed above ground and thelike and is supported, in the absence of other support, upon a quantityof air at superatmospheric pressure, and wherein the weight transferringmeans includes means for transferring to a pile at least a portion ofthe momentum of the base arising from downward movement of the basewithin said range.
 27. A method for driving a pile and the likecomprising the steps of: a. providing an elevatable base, b. disposing apile to be driven substantially vertically through the base with thelower end of the pile in engagement with ground into which the pile isto be driven, c. elevating the base from a lowered position thereofrelative to the ground and the pile, d. applying to the pile at least aportion of the weight of the base including coupling the base to thepile at a position of the base above the lowered position thereof, ande. applying impact force to the upper end of the pile followingapplication of at least a portion of the weight of the base to the pile.28. Apparatus for penetrating a selected elongate member into an earthformation comprising a platform, driving means carried by the platformoperable upon a substantially vertically disposed selected elongatemember located adjacent the platform to urge the member to penetrate anearth formation below the platform, skirt means carried by the platformoperable in combination with ground and the like below the platform forenclosing a space below the platform, means communicating with the spaceoperable for generating subambient pressure within the space thereby toapply to the platform a downward force, and means cooperable between theplatform and the member for transferring a substantial portion of saidforce to the member.
 29. Apparatus according to claim 28 wherein theelongate member is a pile.